Traditional automatic transmission controls shift gears according to preselected shift maps, e.g. at specified ground speeds, even if the engine is at full speed and full throttle. Gear shifts according to this method are inefficient and result in excessive wear to driveline components. More specifically, the transmission clutches must absorb kinetic energy generated by the engine during the gear changes. Such systems can exhibit excessive shift shock when the new gear is engaged due to the difference between the engine speed and the transmission speed in the new gear.
In view of these problems, vehicle manufacturers have developed control systems that are commonly referred to as integrated engine and transmission controllers. These systems function to reduce engine power during shifts to obtain satisfactory shift characteristics and increase the durability of the transmission clutches. Such systems generally reduce the engine speed during the shift by retarding ignition timing, reducing fuel injection or through a combination of both. Examples of integrated controllers are disclosed in U.S. Pat. Nos. 4,226,447; 4,355,550; 4,370,903; and 4,403,527.
Other types of integrated engine and transmission controllers are also known. For example U.S. Pat. No. 5,323,667 (hereafter "the '667 patent"), entitled "Integrated Engine and Transmission Control System" is directed towards providing an integrated engine and transmission controller which exhibits superior performance with respect to other known systems. It achieves that performance in part by regulating engine speed to a speed that is a predetermined amount above the synchronization speed in the new gear during upshifts. During downshifts, the control system regulates engine speed to a speed that is a predetermined amount below the synchronization speed in the new gear. The control holds that predetermined speed for a fixed, empirically determined time period that approximates the time required to engage the new gear.
The control system disclosed in the '667 was a significant improvement over prior controls. However, as can be appreciated, since the control regulates the engine speed for a fixed time that only approximates the actual time required to engage the new gear, there are instances where the approximation may be too long, resulting in reduced performance. Similarly, there may be instances where the approximation is too short, resulting in increased engine speeds prior to full engagement of the new gear, thereby subjecting the transmission to measured torques.
It would be preferable to have a control system that could measure the actual time required to accomplish a gear shift and thereafter modify the time period during which the control issues the engine speed command. The present invention is directed toward overcoming these and other problems associated with the prior art.